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AI detector

Updated June 10, 2026

Software that estimates the probability that a piece of text was generated by an AI language model.

Definition

An AI detector (or AI content detector) analyzes text and outputs a probability that it was machine-generated. Most combine statistical measurements — word predictability (perplexity) and structural variation (burstiness) — with trained classifiers that learned the contrast between human and model corpora. Output is typically an overall percentage plus sentence-level highlighting.

The major ones

In education: Turnitin (inside LMS portals) and GPTZero. In publishing and content work: Originality.ai and Copyleaks. Free quick-checks: ZeroGPT, QuillBot, Sapling, Scribbr. Each is covered in detail in our detector guides.

Accuracy in one paragraph

Good detectors catch most unedited model output and false-flag a meaningful minority of human writing — formal prose and non-native English worst of all. Scores are probabilities, not proof; vendors themselves caution against verdict use. Full treatment: do AI detectors actually work?

Keep reading

Blog

Do AI detectors actually work?

AI detectors are accurate enough to be used everywhere and wrong often enough to ruin someone's week. What independent testing finds, where detectors fail, and how to act on a score.

Glossary

Perplexity

Perplexity measures how predictable text is to a language model. Low perplexity — predictable word choices — is the classic statistical signature of AI-generated text.

AI detector guides

How to pass GPTZero

What GPTZero measures (perplexity and burstiness), why it flags AI text, and a workflow to humanize your writing and verify the score before anyone else checks it.

Blog

Falsely flagged by an AI detector? Here's the playbook

Detectors flag honest writing every day, and non-native speakers worst of all. Why false positives happen, the evidence to gather, and how to defend work you actually wrote.

Humanize it — then verify it

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